A'isha reported that Sauda (Allah he pleated with her) went out (in the fields) in order to answer the call of nature even after the time when veil had been prescribed for women. She had been a bulky lady, significant in height amongst the women, and she could not conceal herself from him who had known her. 'Umar b. Khattab saw her and said:

Sauda, by Allah, you cannot conceal from us. Therefore, be careful when you go out. She ('A'isha) said: She turned back. Allah's Messenger (ﷺ) was at that time in my house having his evening meal and there was a bone in his hand. She (Sauda) cline and said: Allah's Messenger. I went out and 'Umar said to me so and so. She ('A'isha) reported: There came the revelation to him and then it was over; the bone was then in his hand and he had not thrown it and he said:" Permission has been granted to you that you may go out for your needs."
حَدَّثَنَا أَبُو بَكْرِ بْنُ أَبِي شَيْبَةَ، وَأَبُو كُرَيْبٍ قَالاَ حَدَّثَنَا أَبُو أُسَامَةَ، عَنْ هِشَامٍ، عَنْ أَبِيهِ، عَنْ عَائِشَةَ، قَالَتْ خَرَجَتْ سَوْدَةُ بَعْدَ مَا ضُرِبَ عَلَيْهَا الْحِجَابُ لِتَقْضِيَ حَاجَتَهَا وَكَانَتِ امْرَأَةً جَسِيمَةً تَفْرَعُ النِّسَاءَ جِسْمًا لاَ تَخْفَى عَلَى مَنْ يَعْرِفُهَا فَرَآهَا عُمَرُ بْنُ الْخَطَّابِ فَقَالَ يَا سَوْدَةُ وَاللَّهِ مَا تَخْفَيْنَ عَلَيْنَا فَانْظُرِي كَيْفَ تَخْرُجِينَ ‏.‏ قَالَتْ فَانْكَفَأَتْ رَاجِعَةً وَرَسُولُ اللَّهِ صلى الله عليه وسلم فِي بَيْتِي وَإِنَّهُ لَيَتَعَشَّى وَفِي يَدِهِ عَرْقٌ فَدَخَلَتْ فَقَالَتْ يَا رَسُولَ اللَّهِ إِنِّي خَرَجْتُ فَقَالَ لِي عُمَرُ كَذَا وَكَذَا ‏.‏ قَالَتْ فَأُوحِيَ إِلَيْهِ ثُمَّ رُفِعَ عَنْهُ وَإِنَّ الْعَرْقَ فِي يَدِهِ مَا وَضَعَهُ فَقَالَ ‏ "‏ إِنَّهُ قَدْ أُذِنَ لَكُنَّ أَنْ تَخْرُجْنَ لِحَاجَتِكُنَّ ‏"‏ ‏.‏ وَفِي رِوَايَةِ أَبِي بَكْرٍ يَفْرَعُ النِّسَاءَ جِسْمُهَا ‏.‏ زَادَ أَبُو بَكْرٍ فِي حَدِيثِهِ فَقَالَ هِشَامٌ يَعْنِي الْبَرَازَ ‏.‏
Reference : Sahih Muslim 2170 a
In-book reference : Book 39, Hadith 23
USC-MSA web (English) reference : Book 26, Hadith 5395
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